The objective of the present research is to establish the mechanism of the subreaction of protein synthesis, translocation, and its relationship to the other two steps in protein chain elongation. We will approach this problem by first examining the properties and interactions of the ribosome and G factor. Our first objective is to establish the mechanism of uncoupled GTP hydrolysis by this system and to further define the mechanisms by which thiostrepton and fusidic acid inhibit it. On the basis of the information gained from these studies, we shall begin the stepwise reconstruction of the complexes involved in translocation and to correlate this process with that of GTP hydrolysis.